This invention is a novel shut-off means for a hand-held torque tool that cures a deficiency of previous shut-off mechanisms. Prior to this invention, shut-off of the tool has been accomplished using cams to release a cocked mechanism. This cocked mechanism is used to hold open a valve in the power supply circuit to the tool motor. The cams have usually been actuated by relative movement between the motor spindle and the output spindle upon reaching the desired torque. In prior art mechanisms, the relative movement was usually through a spring arrangement that would restore the elements to their initial operating positions upon shut-off. Thus, the cam arrangement would be restored to its initial operating position. One of the inventors named in this case has developed a novel clutch for use in a torque wrench which also allows relative movement between the drive spindle and the output spindle when proper torque is achieved, but does not restore these elements to the initial position. Accordingly, the possibility exists that the cam can stop with its high point in the position for shut-off. When the cam is in that position, the shut-off mechanism cannot reset, but is automatically pushed immediately to the off position upon re-engagement of the output spindle with a fastener. This novel clutch and two prior art shut-off mechanisms are shown and described in U.S. patent application Ser. No. 534,236, filed Dec. 19, 1974 now U.S. Pat. No. 3,955,662 issued May 11, 1976 to which reference is made for a more complete understanding of the clutch operation and the prior art shut-offs.
It is a principal object of this invention to provide a positive, accurate shut-off means for a powered torque wrench.
It is a further object to provide a shut-off means that is responsive to the torque setting in the tool to automatically produce a cessation of the operation of the tool.
It is a further object to provide a shut-off means that will not "hang up" in the off position, which would prevent repetitive operation of the tool.
It is a further object to provide a shut-off means that will limit clutch wear and heating by producing a cessation of operation of the tool immediately upon reaching the set torque.
Another object of this invention is to provide a shut-off mechanism that is relatively straightforward in operation, easy to maintain, and economical to construct.